1. Field of the Invention
The present invention generally relates to semiconductor devices and, more particularly, to a semiconductor device having a plurality of multi-chip modules connected to each other, each of the multi-chip modules having a plurality of input/output terminals.
2. Description of the Related Art
Recently, in the electronic equipment field, a multi-chip module (MCM) has been put into practice. The MCM comprises a thin-film circuit board which can achieve a high-density wiring and functional parts mounted on the thin-film circuit board.
FIG. 1 is a perspective view of a conventional multi-chip module (MCM). The conventional MCM 1 shown in FIG. 1 comprises an MCM board 2, a plurality of functional parts 3 and a plurality of input/output pins 4. The functional parts 3 include a CPU chip for processing data, a cache memory chip for temporarily storing processed data and an interface LSI chip for controlling the input and output of signals in the MCM 1.
Generally, the MCM board 2 of the MCM 1 has a size of a few square centimeters. The MCM board 2 is made of a ceramic material. A thin-film multi-layered circuit is formed on the ceramic material. The functional parts 3 are mounted on the MCM board 2 by means of bump connections, which enables high-density connections. The bumps are made from solder or gold. Each of the bumps has a ball-like shape having a diameter of tens of micrometers. Accordingly, a part having terminals arranged in a grid with a pitch of hundreds of micrometers can be mounted.
According to the above-mentioned structure, a wiring pattern between the MCM board 2 and the functional parts 3 can be made short so as to increase the signal transmission throughput. Thus, the MCM 1 has become popular in the electronic equipment field in which computers requiring a high-speed operation are included.
FIG. 2 is a perspective view of a printed circuit-board unit having a plurality of MCMs 1 shown in FIG. 1. In FIG. 2, the printed circuit-board unit 11 comprises a motherboard 12, a plurality of MCMs 1, a plurality of memory sockets 13 for mounting RAMs, and a plurality of I/O connectors 14 for connecting input/output cables. It should be noted that each of the MCMs 1 shown in FIG. 2 has a height greater than that shown in FIG. 1 since each of the MCMs 1 is usually provided with a heat sink mounted on the functional parts 3.
The printed circuit-board unit 11 is used as a brain of a computer system that requires high-speed data processing. As mentioned above, as computer systems have come to require a high-level function, the number of MCMs used in the printed circuit-board unit has been increasing.
If there is an MCM that satisfies a whole function alone, there is no need to provide the interconnection between the MCMs. However, in practice, such a large MCM is not favored due to low yield rates and large investment required for the manufacturing facility.
FIG. 3 is a side view of a part of the printed circuit board unit 11 shown in FIG. 2. As shown in FIG. 2, wiring patterns 26 and 27 are formed between the MCM 1-1 and the MCM 1-2 mounted on the motherboard 12 so as to interconnect the MCMs 1-1 and 1-2. The wiring patterns 26 and 27 are formed in a thick-film wiring layer formed on the motherboard 12. The signal transmission throughput between the MCMs 1-1 and 1-2 is a major factor in determining the processing capability of the system. Accordingly, lengths of the wiring patterns 26 and 27 are preferably as short as possible so as to achieve a quick signal transmission.
The path of each of the wiring patterns 26 and 27 extends between a terminal of the interface LSI chip 20-1 of the MCM 1-1 and a terminal of the interface LSI chip 20-2 of the MCM 1-2. Each of the wiring patterns 26 and 27 routes one of bumps 23-1 of the interface LSI chip 20-1, a thin-film multi-layer circuit 25-1, a through hole 28-1 of a ceramic board 24-1, one of the input/output pins 4-1, the thin-film multi-layer circuit 25 of the motherboard 12, one of the input/output pins 4-2, a through hole 28-2 of a ceramic board 24-2, a thin-film multi-layer circuit 25-2 and one of the bumps 23-2 of the interface LSI chip 20-2.
Consideration is made to the length of the wiring patterns 26 and 27 with respect to a direction (vertical direction) of the height of the MCMs 1-1 and 1-2 and a direction (horizontal direction) parallel to the mounting surface of the motherboard 12. With respect to the vertical direction, a length of each of the through holes 28-1 and 28-2 of the ceramic boards 24-1 and 24-2 must be a few millimeters, which is equal to the thickness of each of the ceramic boards 24-1 and 24-2, respectively. A length of each of the input/output pins 24-1 and 24-2 must be a few millimeters when a pin grid array (PGA) is used to absorb a distortion generated in the mounting structure between the motherboard 12 and each of the MCMs 1-1 and MCM 1-2.
With respect to the horizontal direction, the path distance between the input/output pins 4-1 of the MCM 1-1 and the input/output pins 4-2 of the MCM 1-2 to be connected to each other is determined by the wiring rule of the motherboard 12. If a distance between the terminal of the interface LSI chip 20-1 is far from the input/output pins 4-1 to be connected as shown in FIG. 3, a long wiring path must be provided.
As mentioned above, in the structure shown in FIG. 3, the wiring path between the MCM 1-1 and the MCM 1-2 must always extend through the motherboard 12. Accordingly, the length of each of the wiring patterns 26 and 27 cannot be shorter than a predetermined length.
In order to reduce the length of the wiring path between the MCMs, a structure in which the MCMs are interconnected by a flexible wiring board 30 as shown in FIG. 4 has been suggested. The flexible wiring board 30 shown in FIG. 4 is a flexible board having a high-density wiring structure formed by thin-film multi layered circuits.
In FIG. 4, each of the wiring patterns 26 and 27 shown in FIG. 3 corresponds to a total of a wiring pattern 32-1 connecting the interface LSI chip 20-1 to the flexible circuit board 30, a wiring pattern 32-2 connecting the the interface LSI chip 20-2 to the flexible circuit board 30 and a wiring pattern 31 extending through the flexible wiring board 30.
The length of the wiring pattern connecting the interface LSI chips 20-1 and 20-2 does not include the lengths of the through holes 28-1 and 28-2 of the ceramic boards 24-1 and 24-2 and the lengths of the input/output pins 4-1 and 4-1 that exist in the structure shown in FIG. 3. Thus, a length of the wiring path along the vertical direction is reduced by a few millimeters.
In the horizontal direction, there is no need to provide the wiring path from the terminal of the each of the interface LSI chips 20-1 and 20-2 to the respective one of the input/output pins 4-1 and 4-2 and the wiring path corresponding to the path in the motherboard 12. Accordingly, the wiring path is shortened by tens of millimeters.
In the structure shown in FIG. 4, the wiring pattern 32 is newly added. However, since the eliminated length of the wiring path extending in the motherboard 12 as shown in FIG. 3 is greater than the newly provided wiring pattern 32, the lengths of wiring patterns shown in FIG. 4 are shorter that that shown in FIG. 3.
However, there is a demand for further increasing the processing throughput due to continuous increase in the processing speed of computer systems. In order to further increase the processing throughput, it is required to further shorten the wiring patterns interconnecting the MCMs.
It is a general object of the present invention to provide an improved and useful semiconductor device in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a semiconductor device having a plurality of MCMs mutually communicating at a higher throughput rate than a conventional one by reducing the length of the signal path between the interface LSI chips of the MCMs.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a semiconductor device comprising: a first multi-chip module having a plurality of functional parts mounted on a circuit board; a second multi-chip module having a plurality of functional parts mounted on a circuit board; a flexible wiring board connecting the first multi-chip module to the second multi-chip module; and an interface part mounted on the flexible wiring board, the interface part controlling input and output signals of the first multi-chip module.
According to the above-mentioned invention, a signal path for transmitting signals between the first multi-chip module and the second multi-chip module is provided by the flexible wiring board. The interface for the signals transmitted between the first multi-chip module and the second multi-chip module is provided by the interface part mounted on the flexible wiring board. Accordingly, there is no need to provide an interface part (interface LSI chip) to each of the first and second multi-chip modules. Thus, the signal path for the signals transmitted between the first multi-chip module and the second multi-chip module is reduced, resulting in an increase in the processing throughput of the semiconductor device as a whole.
Additionally, there is provided according to another aspect of the present invention a printed circuit-board unit comprising a motherboard and the above-mentioned semiconductor device mounted on the motherboard. The printed circuit-board unit according to the present invention has the same advantages as the semiconductor device according to the present invention.
Other objects, features and advantages of the present invention will become more apparent from the following detailed descriptions when read in conjunction with the accompanying drawings.